1. Field of the Invention
The present invention relates to a secondary battery. More particularly, the present invention relates to a secondary battery having improved characteristics for manufacturing the secondary battery.
2. Description of the Prior Art
Recently, electronic appliances having compact sizes with light weight, such as cellular phones, notebook computers and camcorders, have been actively developed and produced. Such electronic appliances are equipped with battery packs so that users can use the electric/electronic appliances in various places even if electric power sources are not separately provided for the electronic appliances. The battery pack includes at least one battery capable of outputting an operational voltage having a predetermined level in order to operate the electronic appliances for a predetermined period of time.
Secondary batteries, which are rechargeable batteries, are currently employed in the secondary pack due to their economical advantages. The secondary batteries include Ni—Cd batteries, Ni-MH batteries and Li secondary batteries, such as Li batteries or Li-ion batteries.
In particular, lithium secondary batteries have an operational voltage of about 3.6V, which is three times higher than that of Ni—Cd batteries or Ni-MH batteries used as power sources for the portable electronic appliances. In addition, the lithium ion secondary batteries have high energy density per unit weight, so the lithium ion secondary batteries are extensively used in the advanced electronic technology fields.
The lithium secondary battery uses lithium-based oxide as a positive electrode active material and carbon as a negative electrode active material. In general, lithium batteries are classified into liquid electrolyte batteries and polymer electrolyte batteries according to the kind of the electrolytes used therefor. The liquid electrolyte batteries are called “lithium ion batteries” and the polymer electrolyte batteries are called “lithium polymer batteries”. In addition, lithium secondary batteries may be fabricated with various shapes, such as cylinder type batteries, square type batteries, or pouch type batteries.
Typically, lithium secondary batteries include a can, a jellyroll type electrode assembly accommodated in the can, a cap assembly coupled to an upper portion of the can to seal the can and a washer coupled to an upper portion of a cap plate provided in the cap assembly.
The cap plate has a centrally located terminal hole into which an electrode terminal is inserted, and has an electrolyte injection hole on one side through which an electrolyte is injected into the can. In addition, a safety vent is formed at the other side of the cap plate. The safety vent may be prepared by forming a hole in the cap plate and sealing the hole with a laminated plate by means of welding, or by forming a recess having a predetermined depth such that the side of the cap plate has a significantly reduced thickness. Thus, the safety vent may be fracturable before internal pressure of the battery rises to a dangerous level or when an explosion occurs in the battery.
In addition, an electrode lead wire is installed at an upper portion of the cap plate in order to electrically connect an external terminal with the electrode terminal. A washer is formed at a center portion thereof with an electrode lead hole for allowing the electrode terminal to make contact with the electrode lead wire so that the electrode terminal is exposed through the electrode lead hole of the washer. The washer is installed on an upper portion of the cap plate in order to prevent short-circuit between the cap plate and the electrode lead wire.
However, according to a conventional secondary battery having the above structure, the washer is made from an opaque material with a symmetrical structure. Thus, it is difficult for a worker to locate the position of the electrolyte injection hole and the safety vent during the fabrication process for the secondary battery if the electrolyte injection hole or the safety vent is covered with the washer. That is, the worker must check the position of the safety vent or the electrolyte injection hole by raising the washer when welding the electrode terminal to the electrode wire, reducing the efficiency of welding work.
In addition, since the electrolyte injection hole is sealed by means of a plug, the washer may loosen on the cap plate due to a protrusion part of the plug protruding from an upper surface of the cap plate. That is, the washer may not remain horizontal on the cap plate, making it difficult to securely fix other components to the battery.